1. Field of the Invention
The present invention relates to a composite material and a process for its production, and more particularly, relates to a fiber reinforced light alloy composite material including alumina-silica fibers as its reinforcing material and a method for producing such a composite material.
2. Description of the Prior Art
In automobiles and aircrafts, in order to save energy by lowering fuel consumption and to increase their operational speed, there have been made various attempts to lighten the structural members of them. As a measure for lightening their structural members, it has been considered to construct them by light alloy materials such as aluminum alloys and magnesium alloys. However, when the structural members of automobiles or aircrafts are made of only such light alloy materials, it is very difficult to ensure such high strength, anti-wearing characteristic, and anti-seizing characteristic of their structures that would sufficiently guarantee their their valid operation. Therefore, it has been attempted to construct these structural members by composite materials of the kind which has a matrix made of aluminum, magnesium or their alloys and is reinforced by fibers such as alumina-silica fibers, crystallized glass fibers, stainless steel fibers, etc., which are incorporated in the matrix.
However, since inorganic fibers as mentioned above are generally much harder than aluminum, magnesium or their alloys forming the matrix, the composite materials which include such hard reinforcing fibers are bound with difficult problems that they can not be readily worked by lathing or the like, and that they cause severe wearing of mating members which are moved relative to and in contact with them. Ironically, these problems are especially serious with respect to the composite materials which include alumina-silica fibers as the reinforcing materials which are highly compatible with aluminum, magnesium or their alloys and which have high thermal resistance. A bundle of alumina-silica fibers include generally about 50 wt.% non-fibered particles, which are called "shot", of various sizes. The diameters of these particles are generally much larger than those of the fibers, and, since the particles are very hard, it is very difficult to work these composite materials which include the alumina-silica fibers as well as these particles, and they cause abnormal wearing of their mating members.
In view of the problems encountered in the prior art with regard to the conventional composite materials having a matrix of aluminum, magnesium or their alloys and reinforcing fibers of inorganic materials, the present inventors had made various composite materials having a matrix of aluminum, magnesium or their alloys and reinforcing means of alumina-silica fibers and after extensive experimental research, have found that the above-mentioned problems could be solved if the virtual density of the non-fibered particles included in the bundle of alumina-silica fibers should be limited within a certain range. Further, the present inventors have also found that, in order to efficiently produce a composite material which has a matrix of aluminum, magnesium or their alloys and is reinforced by a bundle of alumina-silica fibers, the compression strength of the bundle of alumina-silica fibers must be controlled within a range, and that, in order to obtain such certain required compression strength of the bundle of alumina-silica fibers, the amount of inorganic binder must also be controlled within a certain range.